Well, obviously I can not give you a complete tutorial in one sentence, but you have to realize the following. If you'll be happy with the fact that about 80% of the people will see you site the same way and you don't care there are html errors that are differently interpretted by the different browsers (talking bout the other 20%), then just keep it that way. Otherwise, if you do care, and if you have some time you want to spend on that: start reading. Excellent starting point would be: http://www.w3schools.com/html/ and http://tranchant.plus.com/web/html-tutorial/
Once you start making html pages that validate (http://validator.w3.org/), you should have to start reading about Cascading Style Sheets (http://www.w3.org/Style/CSS/). So that's how designers try to work today: valid (x)html with all styling and layout defined in different CSS page, that are included in your html files with one command.
Oh jeah, if you still try to follow the way i suggested yeaterday, then also make sure you set the margins of your table and iframe to 0, forgot to mension that. Success.